OpenCXP is very close to what you've described:
http://www.OpenCXP.orgCurrently in pre-release RFC stage (request for comment) but the official white paper should be released soon.
This looks kind of what I though about, here and there some things I've not figured out that much but look promising, thanks for the link.
It's called a cellphone.
Install a wallet app, load some change onto it, and you're set.
Making merchants accept payments via mobile phone is already happening, not even affiliated with Bitcoin, it's called "mobile payments" and is considered one of the most important markets of the near future, so we don't even need dedicated Bitcoin merchant terminals. All we need is mobile payment solution providers to also prepare for Bitcoin. And they will, because Bitcoin is just the hype of the day when it comes to talking with venture capital.
Since you seem to be from germany too, you will gladly answer the following questions:
1. When was the last time you payed something with mobile payment from your phone
2. What is the ration of you paying with your card/phone
3. Do you really believe that a cellphone is more secure than a card?
4. Do you really believe that paying via cellphone stops people from stealing your data?
5. Do you really believe you will still be able to make anonymous payments via mobile payment when compared to a card which would be more anonymous?
And yeah, mobile payment is a trend and will be the future. However, living in a world where the "tech scene" still talks about how big ecommerce will be and why you should add responsiveness to your homepage, i don't believe that this future is somewhere so close as all people mean it is. Sure, there are some hip trendy stores accepting it, but thats not a majority and i doubt the majority will accept this so soon.